基于自适应虚拟谐波阻抗控制的孤岛微电网谐波均流策略

Harmonic Current Sharing Strategy in Islanding Microgrid Based on Adaptive Virtual Harmonic Impedance Control

孤岛微电网中非线性负载带来了大量谐波,若各并联逆变器连接至公共交流母线的馈线阻抗与其额定容量失配,将使得谐波电流不能在各逆变器间均匀分配。固定虚拟谐波阻抗方法可以有效地提高谐波电流分配精度,但会影响公共交流母线电压质量。因此,提出了一种自动调节虚拟谐波阻抗实现谐波均流的控制策略。各逆变器根据其谐波电流的有效值构造实时变化的虚拟谐波阻抗,建立起谐波电流与虚拟谐波阻抗的自调整关系,重塑系统在谐波域的输出阻抗以匹配馈线阻抗,动态调整谐波电流分配,有效地提高了谐波均流精度,且兼顾了公共交流母线的电压质量,无需检测线路阻抗信息。仿真和实验结果验证了所提策略的可行性。

In islanding microgrid high harmonic current exists due to nonlinear loads. When the feeder impedances connected to the common AC bus for parallel inverters mismatch with their rated capacities, the harmonic current will not be shared evenly among the distributed generating (DG) units. The fixed virtual harmonic impedance method can effectively improve accuracy of harmonic current sharing, but affect the voltage quality at the point of common coupling (PCC). Therefore, an adaptive virtual harmonic impedance method is proposed to improve accuracy of harmonic power sharing among the DG units. In this method, a variable virtual harmonic impedance in real time is constructed by introducing harmonic current information. An adaptive relationship between the harmonic current and the virtual harmonic impedance is established, and the output impedances of the system at harmonic frequencies are reconstructed. Thus the voltage quality at PCC is improved. In addition, the DG feeder impedance does not need to be detected. Simulation and experimental results demonstrate effectiveness of the proposed scheme.